Recent developments in the study of the structure and function of muscle sarcoplasmic reticulum have permitted a resolution of molecular components involved in the Ca ions transport of the membrane. We plan to study: 1) the roles membrane components, particularly the (Ca ions plus Mg ions) activated ATPase and the metal binding protein play in the transport mechanism, 2) interaction of the components of the transport machinery through reconstitution experiments, and 3) organization of the transport machinery in the sarcoplasmic reticulum in situ with the use of immunochemical techniques combined with electron microscopy. The object of this project is to provide information concerning the basic molecular mechanism underlying the regulation of contraction and relaxation by the sarcoplasmic reticulum and to apply it to the understanding of differing functional characteristics of fast and slow skeletal and cardiac muscles and to the disease process of muscle.